Stack mould assembly

ABSTRACT

An injection moulding process for making a toothbrush involving a stack mould assembly of at least three mould blocks ( 1, 2, 3, 4 ) arranged for use along a longitudinal stack axis (A—A), with two end mould blocks ( 3, 4 ), and an intermediate mould block ( 1, 2 ), with part mould cavities ( 11 A,  21, 31, 41, 51 ) in the blocks. Plastic toothbrush skeletons are made in a cavity ( 11 A,  21, 31 ) between the intermediate block ( 1, 2 ) and one end block ( 3 ), then elastomer parts are made in a cavity ( 41, 51 ) between the intermediate block ( 1, 2 ) and the other end block ( 4 ). Preferably the intermediate block ( 1 ) rotates so its part cavity ( 11 A) faces the other end block ( 4 ). Stack mould assemblies ( 1, 2, 3, 4 ) for this process are provided. The assembly ( 1, 2, 3, 4 ) provides a compact mould with high output.

FIELD OF THE INVENTION

This invention relates to a process for making toothbrushes, inparticular an injection moulding process.

BACKGROUND OF THE INVENTION

Toothbrushes are well-known articles and normally comprise a head and agrip handle, generally with a narrowed neck region in between, allarranged along a longitudinal head-handle axis. Normally toothbrushesare made primarily of a hard plastic material, e.g. a polypropylene orstyrol acryl nitrol (“SAN”). Many are so called two-componenttoothbrushes, i.e. comprising parts made of hard plastic, e.g. the headand the main structure or “skeleton” of the handle, and parts made of asofter resilient elastomer or rubbery material, such as a thermoplasticelastomer e.g. Santoprene™ e.g. comprising part of the grip handle, toenhance grip, aesthetic appearance or to influence flexibility. Suchtoothbrushes are disclosed for example in U.S. Pat. No. 5,054,154 andEP-A-0 336 641 among others.

Toothbrushes are normally made by an injection moulding process in whichthe hard plastic material of which their main structure is made isinjected in a fluid state into a first mould cavity which accuratelydefines the shape of the hard plastic part to be formed. The mouldcavity is normally formed in a hard metal (usually steel) mould block,using a process of spark-erosion also known as electro-dischargemachining. Normally when the toothbrush head is formed in such a processpins are provided (“bristle pins”) projecting onto the part of thecavity in which the head is to be formed, to form holes in the plasticmaterial of the head into which tufts of bristles can subsequently befixed. With two component toothbrushes a “skeleton” of hard plastic isfirst made in this way then the skeleton is enclosed in a second mouldcavity and the material of the second component in a fluid state isinjected into this second cavity to form the second component parts.Normally the skeleton is formed with voids to receive this secondmaterial. Normally such injection moulds are mould assemblies comprisingone or more, generally two, mould blocks each with a part mould cavitytherein, which when brought together in the assembled mould define acomplete mould cavity between them. Such processes are well known.WO-A-94/05183, EP-A-0 504 571, EP-A-0 836 923 and DE-A-195 22 122describe such processes and suitable moulding machinery for theirperformance.

Generally such moulding processes involve large and complex machineryand such machines can take up much floor space in a factory. It isdesirable to provide improved moulding machinery for such processes. Socalled stack moulds are known which can be made very compact. Forexample U.S. Pat. No. 5,069,615 discloses a stack mould for makingplastic articles.

SUMMARY OF THE INVENTION

In its broadest aspect this invention provides a process using a stackmould to manufacture a two component toothbrush comprising parts made ofhard plastic, e.g. the head and the main structure or “skeleton” of thehandle, and parts made of a softer resilient elastomer or rubberymaterial, such as a thermoplastic elastomer e.g. comprising part of thegrip handle, to enhance grip, aesthetic appearance or to influenceflexibility. The invention therefore also provides a stack mould adaptedand/or configured to perform such a process.

DETAILED DESCRIPTION OF THE INVENTION

According to this invention in a more specific aspect, a process formaking a toothbrush comprises:

providing a stack mould assembly comprising a stack of at least threemould blocks arranged for use along a longitudinal stack axis,comprising two end mould blocks, and an intermediate mould blocklongitudinally between the two end mould blocks;

there being at least one part mould cavity in a surface of one end mouldblock which mates with a part mould cavity in a facing surface of theintermediate mould block when the one end mould block and theintermediate mould block are brought together to define a first cavityinto which a first moulding material may be injected;

there being at least one part mould cavity in a surface of the other endmould block which mates with a part mould cavity in the intermediatemould block when the said other end mould block and the intermediatemould block are brought together to define a second cavity into which asecond moulding material may be injected;

bringing the one end mould block and the intermediate mould blocktogether to thereby form the first cavity;

injecting a first moulding material being a plastic material suitablefor forming the hard plastic part of a toothbrush head and handle intosaid first cavity;

at least partly enclosing the so formed hard plastic part in a secondcavity formed by bringing together the other end mould block and theintermediate mould block, and injecting a second moulding material,different to the first plastic material and suitable for forming part ofa toothbrush head and/or handle into the second cavity.

Normally before at least partly enclosing the so formed hard plasticpart in the second cavity formed by bringing together the other endmould block and the intermediate mould block, the one end mould blockand the intermediate mould black are separated.

Preferably the so formed hard plastic part is transferred to the partmould cavity in the other end mould block by retaining at least part ofthe so formed hard plastic part in the part mould cavity in theintermediate mould block and rotating the intermediate mould block sothat the surface of the intermediate mould block in which is the partmould cavity faces the surface of the said other end mould block inwhich is the part mould cavity.

According to a preferred embodiment of the process of this invention, aprocess for making a toothbrush comprises:

providing an injection mould comprising;

a first mould block having at least two first part mould cavitiestherein for forming part of a toothbrush head therein, at least one suchfirst part mould cavity being respectively in each of twoopposite-facing surfaces of the first mould block;

a second mould block having at least one second part mould cavitytherein for forming part of a toothbrush handle therein, the first andsecond part mould cavities being capable of mating together to form apart mould cavity defining part of the head and handle of a toothbrushto be formed therein;

a third mould block having at least one third part mould cavity thereinfor forming part of a toothbrush therein, the third part mould cavitycapable of mating together with the first and second part mould cavitiesto form a part mould cavity defining part of the head and handle of atoothbrush to be formed therein;

a fourth mould block having at least one fourth part mould cavitytherein for forming part of a toothbrush, the fourth and first partmould cavities capable of mating together to form a part mould cavitydefining part of the head and handle of a toothbrush to be formedtherein;

the said first, second, third and fourth mould blocks being arranged ina stack mould assembly such that the first and second mould blocks areintermediate in a stack between the said third and fourth mould blocks;

a fifth part mould cavity being provided in a mould block, the fifthpart mould cavity capable of mating together with the first and fourthpart mould cavities to form a part mould cavity defining part of thehead and handle of a toothbrush to be formed therein, the processcomprising the steps of:

(1) bringing the first, second and third mould blocks together so thatthe respective first, second and third part mould cavities therein matetogether to form a mould cavity for forming part of a toothbrush headand handle therein;

(2) injecting a first fluid plastic material into the so-formed mouldcavity to thereby form part of a toothbrush head and handle therein, andallowing the first material to harden;

(3) separating the third mould block from the assembly of first andsecond mould blocks whilst retaining the part toothbrush by its head ina first part mould cavity of the first mould block;

(4) separating the second mould block from the first mould block whilstleaving the part toothbrush retained by its head in a first part mouldcavity of the first mould block;

(5) bringing the first mould block and fourth mould block together so asto enclose the so-formed toothbrush head retained in the first partmould cavity in a cavity formed between the first mould block and thefourth part mould cavity in the fourth mould block;

(6) with the so-formed toothbrush head retained in the cavity betweenthe first and fourth mould blocks, enclosing the so-formed parttoothbrush handle in a handle mould cavity formed by mating a fourthmould cavity in the fourth mould block with a fifth mould cavity in amould block brought together with the fourth mould block,

(7) injecting a second fluid material into the so-formed handle mouldcavity and allowing the second material to harden, so as to form partsof the toothbrush made of the second material;

(8) removing the part formed toothbrush from the mould block assembly.

The above described steps (1) to (8) may be optionally repeated so as toprovide continuous production of toothbrushes.

The so-formed part of a toothbrush head and handle may then be removedfrom the assembly of mould blocks and subjected to further processingsuch as the insertion of bristles into the head, etc. Alternativelybristles may be fixed into the head at an earlier stage, for exampleduring the moulding process in which the head is formed, by the known socalled “anchorless” process of inserting the bristles into the first orsecond part mould cavity so that their ends extend into the cavity, andintroducing the first plastic material into the cavity to form the headand simultaneously weld the ends of the bristles into the head. Suchprocesses are described in for example EP-A-0 142 885, EP-A-0 197 384and EP-A-0 326 634. However, as will be explained later, the bristlingpins used to form the bristle holes in the head into which the bristlesare subsequently inserted provide a convenient way of retaining the partformed toothbrush in a mould cavity. Therefore if the “anchorless”process is used an alternative way of retaining the part formedtoothbrush in a mould cavity may be necessary.

Preferably the third part mould cavity in the third mould block definespart of a toothbrush head and handle.

Preferably the second mould block has the fifth part mould cavitytherein in a surface opposite that in which the second part mould cavityis formed. Alternatively a fifth mould block having the fifth part mouldcavity therein may be provided.

Preferably step (5) involves a rotation operation in which the firstmould block, with the part formed toothbrush retained therein, isrotated, suitably through 180° so that its first part mould cavity(ies)in which the part formed toothbrush head is retained faces the fourthmould block. To facilitate such a rotation operation it is necessary toensure that the mould blocks are sufficiently far apart that the partformed toothbrush retained in the first mould block does not collidewith any other mould block or any other part of the machinery involved.

Preferably the first mould block has a surface opposite to that in whichthe first part mould cavity is formed, and in the opposite surface thereis one or more further first part mould cavity. Such further first partmould cavity is suitably identical to the first part mould cavity. Withsuch a construction, preferably step (6) involves an operation in whichat least one empty further first part mould cavity, in the opposite faceto that on which is/are situated the first mould cavity(ies) in which apart formed toothbrush is retained, is brought together with an emptysecond part mould cavity in a second mould block. Preferably in thisoperation the empty first, second and third mould blocks fit together sothat the respective further first, second and third part mould cavitiestherein mate together form a mould cavity for forming part of atoothbrush head and handle therein, i.e. to perform a step (1) asdescribed above. In such a way, steps (1) and (6) may advantageously beperformed substantially simultaneously, and also injection steps (2) and(7) may also be performed substantially simultaneously using the firstand further first part mould cavities on opposite sides of the firstmould block, facilitating a high-throughput process.

Preferably, for example in step (3), the toothbrush head is retained inthe first part mould cavity by bristle pins projecting into the firstpart mould cavity. Preferably the head is subsequently released from thefirst part mould cavity by the withdrawal of these bristle pins. Mouldsin which such bristle pins can be withdrawn are generally known.

Preferably injection steps (2) and (7) are hot runner injection mouldingsteps. Hot runner moulding is a well known process.

Each of the said mould blocks may have a multiple of the respectiveabove-mentioned part mould cavities, which may be used in parallelsimultaneous operation. Mould blocks with multiple cavities therein arewell known in the toothbrush industry.

Preferably the second material injected in step (7) is a thermoplasticelastomer material, of a known type for use with two-componenttoothbrushes.

Suitable plastics materials for use as the first material include thosewith a modulus of elasticity of at least about 500 Mpa, preferably atleast about 1000 Mpa, these being conventional in the toothbrush art.Suitable materials include for example, polyamides and polypropylenes.An example of a suitable polyamide is the material ‘Ultramid B3™’(marketed by BASF, Federal Republic of Germany), having a modulus ofelasticity (DIN 53452) of 3000. An example of a suitable polypropyleneis the material ‘Novolene 1100 HX™’ (marketed by BASF, Federal Republicof Germany), which is a homopolymer and has a modulus of elasticity (DIN53457) of 1400. Such a polypropylene homopolymer may optionally be usedin admixture with a polypropylene block co-polymer, such as the material‘Novolene 2500HX™’ (marketed by BASF, Federal Republic of Germany), forexample in an 80:20 mixture by weight (1100 HX:2500 HX). Other suitablepolypropylenes include Polypropylene PM 1600™ (marketed by Shell) andhaving a modulus of elasticity (ISO 178) of 1500 Mpa and Apryl 3400 MAI™from Elf Atochem.

Preferably the second moulding material is an elastomeric material, forexample a thermoplastic elastomer. The term “elastomeric material” asused herein is synonymous with such terms as “elastomer”, “elastomermaterial”, “rubber” and “rubbery material”. The term includes syntheticand natural elastomers. The term includes materials which on compressiondeform and spring back immediately or very quickly on release of thepressure. Preferably the elastomeric material has a hardness from about10 to about 90 Shore A, more preferably 30 Shore A or greater. Suitableelastomeric materials include those available under the trade namesMegol and Santoprene, and silicone elastomeric materials may also beused. Other suitable elastomeric materials are disclosed in the state ofthe art referred to above.

Suitably the moulding conditions in step (7) are such that the secondmaterial binds to the first plastic material. Suitable condition areknown.

The invention also provides a stack mould assembly comprised of two endmould blocks and an intermediate mould block longitudinally between thetwo end mould blocks, there being at least one part mould cavity in asurface of one end mould block which mates with a part mould cavity in afacing surface of the intermediate mould block when the one end mouldblock and the intermediate mould block are brought together to define afirst cavity, corresponding to the shape of part of a toothbrush, intowhich a first moulding material may be injected, there being at leastone part mould cavity in a surface of the other end mould block whichmates with a part mould cavity in the intermediate mould block when thesaid other mould block and the intermediate mould block are broughttogether to define a second cavity, corresponding to the shape of partof a toothbrush, into which a second moulding material may be injected.

The invention also provides a stack mould assembly suitable forperforming a process according to the preferred aspect of the inventionas described above.

Such a stack mould assembly may comprise:

a first mould block having at least two first part mould cavitiestherein for forming part of a toothbrush head therein, at least one suchfirst part mould cavity being respectively in each of twoopposite-facing surfaces of the first mould block;

a second mould block having at least one second part mould cavitytherein for forming part of a toothbrush handle therein, the second partmould cavity and first part mould cavity being capable of matingtogether to form a part mould cavity defining part of the head andhandle of a toothbrush to be formed therein;

a third mould block having at least one third part mould cavity thereinfor forming part of a toothbrush therein, the third part mould cavitycapable of mating together with the first and second part mould cavitiesto form a part mould cavity defining part of the head and handle of atoothbrush to be formed therein;

a fourth mould block having at least one fourth part mould cavitytherein for forming part of a toothbrush, the fourth and first partmould cavities capable of mating together to form a part mould cavitydefining part of the head and handle of a toothbrush to be formedtherein;

the said first, second, third and fourth mould blocks being arranged inthe stack mould assembly such that the first and second mould blocks areintermediate in a stack between the said third and fourth mould blocks;

a fifth part mould cavity being provided in a mould block, preferably inthe second mould block, the fifth part mould cavity capable of matingtogether with the first and fourth part mould cavities to form a partmould cavity defining part of the head and handle of a toothbrush to beformed therein.

The invention also provides respective first, second, third, fourth andoptional fifth mould blocks having respective part mould cavitiestherein, suitable for use in the stack mould assembly described above.

The invention also provides a toothbrush manufacturing machineconstructed to use the above-described process and/or incorporating theabove-mentioned first, second, third and fourth mould blocks and/or anassembly thereof.

The invention also provides toothbrushes being a product of theabove-described process and/or machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of non-limiting example onlywith reference to the following drawings, of which:

FIG. 1 shows typical longitudinal and cross sections of a typicaltwo-component toothbrush.

FIGS. 2–9 show schematically an assembly of mould blocks and their usein a process of this invention.

Features shown in FIGS. 1–9 are listed and identified below:

Two component toothbrush 101 (generally)

Head 102

Grip handle 103

Neck 104

Hard plastic skeleton 105, with upper and lower surfaces 105A, 105B.

Elastomeric part 106, with top and bottom surfaces 106A, 106B.

Reinforcing flanges 107

Apertures 108

Bristle holes 109

First mould block 1

Opposed surfaces 1A, 1B

First part mould cavities 11A, 11B

Second mould blocks 2

Surfaces 2A

Second mould cavities 21

Third mould block 3

Third part mould cavities 31

Surface 3A

Injection ports 32

Fourth mould block 4

Fourth part mould cavities 41

Surface 4A

Injection ports 42

Surface 2B

Fifth mould cavities 51

Mould cavity 11,21,31

Mould parting lines 123, 124

Bristle pins 13

Cavity 11,41

Handle mould cavity 41,51

Referring to FIG. 1, a two component toothbrush 101 (generally)comprises a head 102, a grip handle 103, and a neck region 104 inbetween, all arranged along a longitudinal head-handle axis. Thetoothbrush 101 comprises a hard plastic skeleton 105, comprising thehead 102, neck 104 and part of the handle 103, and a second componentelastomeric part 106, forming a grip-enhancing pad on the handle.Internally the grip handle 103 includes reinforcing flanges 107 (suchflanges are known in the art, e.g. from the applicant's toothbrusheslaunched in 1993) to stiffen the handle 103, and apertures 108 which putupper and lower surfaces 105A and 105B of the skeleton 105 intocommunion. There are bristle holes 109 in the head 102, into whichbristles (not shown) may subsequently be inserted.

Referring to FIG. 2 an assembly of injection mould blocks is shown. Thisassembly is a stack mould assembly arranged along a longitudinalstacking axis A—A.

The stack comprises a first mould block 1, which has two opposedsurfaces 1A, 1B facing in 180° opposite directions. Surface 1A has aplurality (four are shown, there may be more or less) of first partmould cavities 11A therein for forming part of a toothbrush headtherein. Opposite surface 1B has a plurality (four are shown, there maybe more or less) of further first part mould cavities 11B therein forforming part of a toothbrush head therein. Surfaces 1A and 1B areidentical. FIG. 2B shows a surface 1A in plan view, and it is seen thatthese part mould cavities 11A are arranged in a tip-to-tip relationship,i.e. with their head-handle axis directions aligned in 180° oppositedirections.

FIG. 2 also shows two second mould blocks 2. These mould blocks 2 can bebrought together with first mould blocks 1 at mould parting line 123.Mould blocks 2 each have surfaces 2A which face surfaces 1A along thestacking axis A—A and mate when first and second blocks, 1 and 2 arebrought together as shown in FIG. 3. Mould blocks 2 have a multiple ofsecond part mould cavities 21. Four are shown, there may be more orless, but corresponding with the number of part mould cavities 11A.These part mould cavities 21 define the shape of part of the skeleton ofa toothbrush handle facing in the bristle direction, i.e. the topsurface 105A shown in FIG. 1. It is seen that with the first and secondmould blocks 1 and 2 brought together at part line 123, the part mouldcavities 21 come together to mate with part mould cavities 11A, meetingthe part mould cavities 11A at a place corresponding to the neck region104 to thereby define the shape of part of a toothbrush skeleton 105 tobe formed therein.

FIG. 2 also shows a third mould block 3. Mould block 3 has a multiple(four are shown, there may be more or less, but corresponding with thenumber of part mould cavities 11A and 21) of third part mould cavities31 therein for forming part of a toothbrush head and handle therein.These part mould cavities 31 define the shape of part of the skeleton105 of a toothbrush handle facing in the opposite direction to thebristle direction, i.e. the lower surface 105B shown in FIG. 1. Thirdmould block 3 has a surface 3A which faces surfaces 1A and 2A and can bebrought together with mould blocks 1 and 2 so that surfaces 1A, 2A and3A meet at parting line 123, and part mould cavities 11A, 21 and 31 mateto form a complete mould cavity defining the shape of part of theskeleton 105 of a toothbrush. Mould block 3 also includes injectionports 32 via which a fluid plastic material may be introduced.

FIG. 2 also shows a fourth mould block 4. Fourth mould block 4 has asurface 4A. Mould block 4 has a plurality (four are present, there maybe more or less, but corresponding with the number of part mouldcavities 11A and 21) of fourth part mould cavities 41 in surface 4Atherein for forming part of a toothbrush therein. These part mouldcavities 41 define the shape of part of the elastomer grip pad 106 of atoothbrush handle facing in the opposite direction to the bristledirection, i.e. the bottom surface 106B shown in FIG. 1. Mould block 4also includes injection ports 42 via which a second fluid plasticmaterial may be introduced.

Second mould blocks 2 have a surface 2B facing in a 180° oppositedirection to surface 2A. In surface 2B are located a plurality (four arepresent, there may be more or less, but corresponding with the number ofpart mould cavities 11 and 21) of fifth part mould cavities 51. Thesepart mould cavities 51 define the shape of part of the elastomer grippad of a toothbrush handle facing in the bristle direction, i.e. the topsurface 106A of the grip pad 106 shown in FIG. 1.

It is seen in the above description and drawings that in the mouldassembly shown in FIG. 2, the third (3) and fourth (4) mould blockscomprise the respective first and second mould blocks, and thesub-assembly of first (1) and second (2) mould blocks comprises anintermediate third mould block of the broadest aspect of the inventionas defined above.

The mould assembly shown in FIG. 2 is used in the process of theinvention to make two component toothbrushes as follows.

Referring to FIG. 3, steps (1) and (2) are shown. In FIG. 3A the first1, second 2 and third 3 mould blocks are brought together by relativemovement in the direction shown by arrows, so that the respective first11A, second 21 and third 31 part mould cavities therein together form amould cavity 11A,21,31 for forming part of the skeleton 105 of atoothbrush head and handle therein. In this operation the surfaces 1A,2A and 3A of mould blocks 1, 2 and 3 meet at the parting line 123.

As shown in FIG. 3B a fluid plastic first material has been injected viainjection ports 32 into the so-formed mould cavity 11A,21,31 to therebyform the skeleton 105 of a toothbrush head and handle therein. Thisfirst material is then allowed to harden. In FIGS. 2 and 3 bristle pins13 are shown which project into the cavity 11A,21,31 so that bristleholes 109 are left in the so-formed head 102.

Also as shown in FIG. 3B, prior to the injection of plastic material viaport 32, the fourth mould block 4 is brought together to form a stackwith the assembly of mould blocks 1, 2 and 3. In this operation, surface4A of mould block 4 comes into contact with respective surfaces 1B and2B of mould blocks 1 and 2, being the surfaces of blocks 1 and 2opposite surfaces 1A, 2A in which the part mould cavities 11A, 21A areformed. This enables a clamping force F to be applied in the directionof the arrows shown to thereby enable the assembly to withstand thepressure generated in the cavity 11A, 21, 31 by the injection of theplastic material.

Referring to FIG. 4, step (3) is shown. The third mould block 3 isseparated from the assembly of first 1 and second 2 mould blocks whilstretaining the skeleton 105 of the toothbrush, comprising both head andhandle parts, in the first mould block 1 by its head 102. This isachieved by relative movement of the mould blocks 1, 2 and 3 in thedirection shown by arrows. The toothbrush skeleton 105 is retained inmould block 1 by means of bristle pins 13 embedded in the formedtoothbrush head 102. These bristle pins 13 are retractable by amechanism (not shown) of known type within block 1.

As part of the same operation the fourth mould block 4 is withdrawn fromthe assembly of mould blocks 1 and 2, i.e. by relative motion in thedirection indicated by the arrows.

Referring to FIG. 5, step (4) is shown. The second mould blocks 2 areseparated from the first mould block 1 whilst leaving the skeleton 105of the toothbrush retained by its head 102 in a first part mould cavity11A of the first mould block 1, by means of bristle pins 13 embedded inthe formed toothbrush head 102. This separation is achieved by a motionof the second mould block 2 as shown by the arrows, being a firstmovement in the direction A—A followed by a movement transverse todirection A—A.

Referring to FIG. 6, step (5) is shown. In FIG. 6A the first mould block1 has been rotated through 180° in the plane of the drawing, so thatsurface 1A in which its first part mould cavity(ies) 11A are formed andin which the part formed toothbrush head 102 is retained faces thefourth mould block 4. By this rotation it is seen that surface 1B ofmould block 1, in which are the further first mould cavities 11B, nowface the third mould block 3. The second 2 and third 3 mould blocks,(and the fourth mould block 4) must be sufficiently clear of therotating first mould block 1 that the retained skeleton(s) 105 thereincan rotate freely as shown.

The first mould block 1 and fourth mould block 4 are brought together soas to partly enclose the part formed toothbrush 105 retained by its head102 in the first part mould cavity 11A in a cavity 11A,41 formed betweenthe first mould block 1 and a fourth part mould cavity 41 in the fourthmould block 4.

Referring to FIG. 7, step (6) is then performed. As shown in FIG. 7, thepart-formed toothbrush handle, i.e. the part of skeleton 105 whichcomprises handle 103 is enclosed in a handle mould cavity 41,51 formedbetween a fourth mould cavity 41 in the fourth mould block 4 and a fifthmould cavity 51 in a second mould block 2. This is achieved by amovement of the second mould block 2 as shown by the arrows, so thatsurfaces 1A, 2B and 4A of respective mould blocks 1, 2 and 4 meet.

As shown in FIG. 8 step (7) is now performed by injecting a fluid secondmaterial, an elastomeric material, into the so-formed handle mouldcavity 41, 51 via injection ports 42. Not shown for simplicity in FIGS.2–8 is that part mould cavities 41 and 51 are shaped so as to definevoids around the outer surface of a skeleton 105 when enclosed therein,into which the second material may flow upon being injected into cavity41,51 to form the elastomer parts 106 of the toothbrush 101. This secondmaterial is then allowed to harden.

Also as shown in FIG. 8, prior to the injection of plastic material viaports 42, the third mould block 3 is brought together to form a stackwith the assembly of mould blocks 1 and 2. This enables a clamping forceF to be applied in the direction of the arrows shown to thereby enablethe assembly to withstand the pressure generated in the cavity 41,51 bythe injection of the elastomer material 106.

Also the respective further first 11B, second 21 and third part mouldcavities 31 therein together form a mould cavity 11B, 21, 31 for formingpart of a toothbrush head and handle therein in a manner identical tosteps (1) and (2) as described with reference to FIG. 3 above, so thatstep (1) can be repeated to form further skeletons 105A therein. In sucha way, steps (1) and (6) may advantageously be performed substantiallysimultaneously.

The mould block 4 may then be separated from the assembly of mouldblocks 1 and 2 and the bristle pins 13 withdrawn from the heads 102 toallow step (8) to take place, i.e. ejecting or allowing the toothbrushesto fall from the mould block assembly. Conventional ejector pins (notshown) may also be used to urge the so-formed toothbrushes out of thepart mould cavities 41,51, and/or the part mould cavities 11A, 11B inmould block 1.

The mould blocks 1, 2 and 3 may also be separated, i.e. in a step (3) asdescribed above, and steps (4), (5) etc. may then be performed on the soformed skeletons 105A.

The so-formed toothbrushes may then be subjected to finishingoperations, e.g. the insertion of bristles into bristle holes 109. Thisseparation of the mould assembly returns the assembly to theconfiguration shown in FIG. 2, enabling the above described steps (1) to(8) to be optionally repeated so as to provide continuous production oftoothbrushes.

FIG. 9 shows a mode of operation of the process of the invention inwhich injection steps (2) and (7) are being performed with the mouldassembly stacked together as shown in FIG. 8. These injection steps (2)and (7) may be performed substantially simultaneously, that is the firstmaterial may be injected via ports 32 into cavity 11A, 21, 31 whilst thesecond fluid material is injected substantially simultaneously intocavity 41,51 via port 42. Thereafter the mould block 4 may be separatedfrom the assembly of mould blocks 1 and 2, and the toothbrushes formedin the cavity 41,51 may be removed as described above, but leaving thepart formed toothbrushes formed in part mould cavities 11,21,31 retainedby their heads as in FIG. 4 to result in a configuration of mould blocksas shown in FIG. 4, and the above described sequence of steps from step(3) onwards may be performed again in a continuously repeated operation.

The various mould blocks 1, 2, 3, 4 may be constructed in standard waysand operated by standard machinery known in the art of toothbrushmanufacture, and the overall process may be automated. Each of the mouldblocks mentioned herein may themselves comprise a sub-assembly of partmould blocks suitably fastened together.

1. A stack mould assembly (1, 2, 3, 4) comprising; a first mould block (1) having at least two first part mould cavities (11A) therein for forming part of a toothbrush head therein, at least one such first part mould cavity (11A) being respectively in each of two opposite-facing surfaces (1A, 1B) of the first mould block (1); a second mould block (2) having at least one second part mould cavity (21) therein for forming part of a toothbrush handle therein, the first (11A) and second (21) part mould cavities capable of mating together to form a part mould cavity (11A, 21) defining part of the head and handle of a toothbrush to be formed therein; a third mould block (3) having at least one third part mould cavity (31) therein for forming part of a toothbrush therein, the third part mould cavity (31) capable of mating together with the first and second part mould cavities (11A, 21) to form a part mould cavity (11A, 21, 31) defining part of the head and handle of a toothbrush to be formed therein; a fourth mould block (4) having at least one fourth part mould cavity (41) therein for forming part of a toothbrush, the fourth part mould cavity (41) and first part mould cavity (11A) being capable of mating together to form a part mould cavity (11A, 41) defining part of the head and handle of a toothbrush to be formed therein; the said first (1), second (2), third (3) and fourth (4) mould blocks being arranged in a stack mould assembly such that the first (1) and second (2) mould blocks are intermediate in a stack between the said third (3) and fourth (4) mould blocks; a fifth part mould cavity (51) being provided in a mould block (2), the fifth part mould cavity (51) capable of mating together with the first and fourth part mould cavities (11A, 41) to form a part mould cavity (41, 51) defining part of the head and handle of a toothbrush to be formed therein.
 2. A stack mould according to claim 1 wherein the third part mould cavity in the third mould block defines part of a toothbrush head and handle.
 3. A stack mould according to claim 1 wherein the fifth part mould cavity is formed in the second mould block in a surface of the second mould block opposite that in which the second part mould cavity is formed.
 4. A stack mould according to claim 1 wherein the first mould block is mounted for rotation relative to the third and fourth mould blocks so that the first part mould cavity(ies) in the first mould block may be rotated to face the fourth mould block.
 5. A stack mould according to claim 1 wherein the first mould block has a surface opposite to that in which the first part mould cavity is formed, and in the opposite surface there is one or more further first part mould cavity.
 6. A stack mould according to claim 5 wherein the further first part mould cavity is identical to the first part mould cavity.
 7. A stack mould according to claim 6 wherein at least one further first part mould cavity may be brought together with a second part mould cavity in a second mould block.
 8. A stack mould according to claim 7 wherein when at least one further first part mould cavity is brought together with a second part mould cavity in a second mould block, the first, second and third mould blocks fit together so that the respective further first, second and third part mould cavities therein mate together form a mould cavity for forming part of a toothbrush head and handle therein.
 9. A stack mould according to claim 2 wherein the fifth part mould cavity is formed in the second mould block in a surface of the second mould block opposite that in which the second part mould cavity is formed. 